Burning rate detector



April 18, 1967 N. P. WILLIAMS, JR

BURNING RATE DETECTOR Filed Jan. 10, 1964 35 PHOTOCELL :l' i as a I; L L: 3| 20 I I7 23 l 1 2o EEEEEEIEI 22 1 I8 I2 I6 9 FUEL 24 I5 SAMPLE I I4 I I i 4 l I 4 l 37 1 I r I l 37 3 34 T' l PHOTOCELL Nathan F? Williams, Jr.

INVENTOR. W M y W .1. W M JW 6 M United States Patent Office 3,315,08l Patented Apr. 18, 1967 3,315,081 BURNING RATE DETECTUR Nathan P. Williams, Jr., Huntsville, Ala., assignor to the United States of America as represented by the decretary of the Army Filed Jan. 10, 1964, Ser. No. 337,105 Claims. (Ql. 250-217) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

This invention relates to an apparatus for obtaining the burning rate of any desired substance with extreme accuracy.

With the advent of modern rocketry it has become more and more important to determine with accuracy the burning rate of the materials used in missile propellants. My invention is particularly adapted to determine the burning rate of solid pyrotechnic materials which are commonly used in missile propellants. In general, my invention concerns a device which provides instantaneous recording of the time at which a burning sample is ignited and an equally accurate recording of the time at which the sample has burned a predetermined distance. Because of their speed and accuracy, photo electric cells have been utilized to actuate a timing means in response to ignition and burn out of a fuel sample. My device is designed to permit an atmosphere of any gas at any desired temperature and pressure to surround the sample during its firing, thereby allowing duplication of the natural environment in which the fuel is to be burned. The device is also provided with a means for connecting the atmospheric supply system to a large surge tank which will maintain the system at a nearly constant atmospheric condition even during burning of the sample.

Prior to my invention, a solid propellant burning rate was determined by placing fuse wire at measured intervals down a strand of propellant and measuring the burning time between the wires. This method is relative- 1y unreliable since the flame front is often propagated down the sides of the propellant strand rather than being restricted to a single burning surface. This unreliability is caused mainly by cracking of the inhibiter along the sides of the strand as well as cracking of the strand itself. The present invention has eliminated inhibitor failure because of the manner in which the sample is retained in its holder. In addition, the sample design also lends itself to easy manufacture without cracks or fissures.

Accordingly, it is an object of this invention to provide a reliable and highly accurate apparatus for determining the burning rate of any desired substance.

A further object of my invention is to provide a burning rate cell in which a desired atmosphere may be provided around the burning sample.

Another object is to provide a burning rate cell which is relatively simple to manufacture and highly, dependable while yet being relatively inexpensive.

Still another object of my invention is to provide a burning rate cell which is extremely safe in operation.

In accordance with this invention, a burning rate detector is provided that includes means for holding a fuel sample, ignition means for igniting the sample, and means for monitoring the time required to burn the sample from the ignition surface to an opposite and outer surface.

This invention together with other objects and advantages will best be understood by reference to the following description and accompanying drawings in which:

FIGURE 1 is a sectional view of my device showing the general arrangements of the various components as well as the manner of connection of the testing unit to a timing mechanism.

Referring now to FIGURE 1, the burning rate cell 1 consists of a housing 2 which is closed at one end by means of a mounting plate 3 held in place by a plate retainer 4. The housing is designed to operate under great variances of pressure and temperature. An O-ring seal 5 is thus provided to prevent leakage between the mounting plate and the housing. The housing is provided with an atmosphere inlet connector 6 and a surge tank connector 7. The inlet may be connected to an atmosphere supply system which will provide atmosphere chamber 8 with a chosen gas at predetermined conditions of temperature and pressure. In situations where a constant condition is required in the atmosphere chamber a surge tank may be connected to connector 7, thus'providing the desired volume to absorb temperature and pressure variations caused by burning in the atmosphere chamber. A sample holder 9 consists of three distinct portions; an ignition chamber 11, a sample receiver r12 and a burn out chamber 13. The holder is also provided with vents 14 which are normally closed by check valves 15 and are actuated in response to an increase of pressure within the sample holder. When in a closed position check valves 15 prevent light communication between burnout chamber 13 and atmosphere chamber 8. A fuel sample 16 is generally held in place by a sample retainer 17 but may of course be retained by other means such as an adhesive. An igniter 18 is placed immediately atop the fuel sample and is generally ignited electrically by passing a current through igniter connectors 19, wires 20, and igniter probes .21. Probes 21 are held in place by an igniter cap 22 which is vented at 23. In the event that the sample to be tested is translucent a light shield 24 may be provided immediately below the sample to prevent light from entering burn out chamber 13 before the flame emerges from the lower or burnout surface of sample 16. A thin layer such as aluminum foil has been found to be satisfactory for this purpose as it acts as a. perfect light shield, yet the advancing flame will penetrate its thickness instantaneously.

A timer 40 is provided to determine the exact time required to burn from the ignition surface of sample 16 to the burn out surface. Timer 40 is provided with electrically actuated starting and stopping mechanisms 31 and 32 respectively. A signal for actuating the starting mechanism is provided by photoelectric cell 33, the signal being transmitted by wires 34 and 35. The photoelectric cell is sealed in housing 2 and its light sensitive surface is protected by a transparent plate 36. A photoelectric cell 34 is mounted on the opposite end of housing 2 in a similar manner and is protected by transparent plate 37. The signal emitted from this photoelectric cell is transmitted through wires 37 and 38 to actuate the stopping mechanism 32 of the timer.

In operation of the device, a sample is inserted in the receiver portion of sample holder 9 and held rigidly in place by retainer 17. igniter 18 is then placed in con tact with the ignition surface of the sample. To initiate the test, an electrical charge is directed through igniter connectors 19, wires Ztl and igniter probes 2-1 to fire igniter 13 which in turn causes immediate burning on the ignition surface of the sample. At the instant the ignition surface of the fuel sample is ignited the light of the ignition flame is detected by photoelectric cell 3-3 which :actuates the starting mechanism 31 of the timer. The timer continues to operate and records the elapsed time. The instant the flame emerges from the burnout surface of the sample the resultant light will actuate photoelectric cell 34 which in turn operates the timer stopping mecha nism. The total elapsed time required to burn completely through the sample is thus recorded. In the event that a rapid rise of pressure should occur within the burnout chamber check valves 15 will release the excess pressure into atmosphere chamber 8 and then into a surge tank via connector 7. The conditions within chamber 8 may of course be controlled by supplying the desired atmosphere chamber 8 and then into a surge tank via connector 7. The conditions within chamber 8 may of course be controlled by supplying the desired atmosphere to the chamber through inlet 6.

From the above description, it will be seen that the device provides instant actuation of the timer both in its initiating stage and its terminating stage. It will also be noted that due to the design of the sample holder flame propagation is eliminated along the lateral surfaces of the fuel sample. It is apparent that the device is not limited to actuation of a timer of a mechanical type alone but rather a calibrated camera or other type of timing mechanism could also be actuated with only minor modifica tions.

The foregoing is a description of the preferred embodimen-t. The following claims are intended to include those modifications and variations that are within the spirit and scope of the invention.

I claim:

11. A burning rate cell comprising means for holding a flammable test sample, said sample having an ignition surface and a burnout surface, means for igniting said ignition surface, a timer for recording the time required for burning through the sample from the ignition surface to the burnout surface thereof, means mounted relative to said holding means, in facing relation to said ignition surface, and immediately responsive to ignition of said sample for turning on said timer, and means facing the burnout surface of said sample and responsive to a flame emerging on the burnout surface of said sample for turning off said timer.

2. A device as set forth in claim 1 wherein said means for holding the test sample comprises; an ignition chamber, a sample receiver and a burnout chamber, at least one pressure vent in said burnout chamber and a light shield separating said sample receiver and burnout chamber.

3. A device as set forth in claim 2 wherein said actuating and deactuating means comprise light sensitive signal means in light communication with respective ignition and burnout surfaces of said sample.

4. A device as set forth in claim 3 wherein said holding means is mounted in a chamber of a housing, and said housing is provided with atmosphere inlet means whereby gas may be supplied to said cell at predetermined conditions of temperature and pressure.

5. A device as set forth in claim 4 wherein said housing is provided with means for connection of the interior of said housing to a surge tank,

6. A burning rate cell comprising a housing, holder means mounted in said housing for mounting a test sample in said housing, ignition means mounted relative to said holder means for igniting an ignition surface of said test sample, a timer, means facing said ignition surface and connected to said timer for turning on said timer in response to ignition of said ignition surface of said test sample, and means for turning olf said timer in response to burning through the opposite and outer surface of said test sample.

'7. A device as set forth in claim 6 wherein said actuating and deactuating means comprise a pair of light responsive signal means one of which is actuated in response to the light of ignition on one surface of said test sample, the other of which is actuated in response to the light emitted when burning has progressed from said ignition surface through the sample to the opposite surface thereof, said one of said light responsive signal means being mounted relative to said housing in facing relation to the ignition surface of said test sample, and said other of said light responsive signal means being mounted relative to said housing in facing relation to the opposite surface of said test sample.

8. A burning rate unit comprising a housing, a sample holder mounted in said housing, said sample holder having an ignition chamber, a sample receiver and a burnout chamber, means for venting said burnout chamber to the interior of said housing, means for igniting said test sample, a pair of photoelectric cells mounted on said housing, one of said photoelectric cells, being in light communication with the interior of said housing, the other of said photoelectric cells being in light communication with the interior of said burnout chamber, said sample receiving portion of said sample holder providing the only light communication between the interior of said housing and said burnout chamber.

9. A device as set forth in claim 8 which further includes means attached to said housing for supplying gas under predetermined conditions of temperature and pressure to the interior of said housing.

10. A device as set forth in claim 9 wherein passage means are provided in said housing for attachment to a surge tank.

References Cited by the Examiner UNITED STATES PATENTS 1,755,970 4/1930 Singleton 250--217 X 2,977,479 3/1961 Lauer 250-217 X 3,201,978 8/1965 Fitzgerald et a1. 250-227 X RALPH G. NILSON, Primary Examiner.

J. D. WALL, Assistant Examiner, 

1. A BURNING RATE CELL COMPRISING MEANS FOR HOLDING A FLAMMABLE TEST SAMPLE, SAID SAMPLE HAVING AN IGNITION SURFACE AND A BURNOUT SURFACE, MEANS FOR IGNITING SAID IGNITION SURFACE, A TIMER FOR RECORDING THE TIME REQUIRED FOR BURNING THROUGH THE SAMPLE FROM THE IGNITION SURFACE TO THE BURNOUT SURFACE THEREOF, MEANS MOUNTED RELATIVE TO SAID HOLDING MEANS, IN FACING RELATION TO SAID IGNITION SURFACE, AND IMMEDIATELY RESPONSIVE TO IGNITION OF SAID SAMPLE FOR TURNING ON SAID TIMER, AND MEANS FACING THE BURNOUT SURFACE OF SAID SAMPLE AND RESPONSIVE TO A FLAME EMERGING ON THE BURNOUT SURFACE OF SAID SAMPLE FOR TURNING OFF SAID TIMER. 